The biggest money makers for the song 's use would be something like a car advertisement.

By erasing history, they are also preventing Fantasia from possibly becoming public domain in the future. If they succeed at doing that, that's a 100 million to 1 billion dollar save for them. I don't want to screw with anyone when that amount of money is involved, but stealing culture is different.
They can't own Bach, they can't own the Sorcerer's Apprentice, they can't own sugar plum fairy or A Night on Bald Mountain -- who did created all that beautiful animation? Are they getting royalties? Are the composer's families getting royalties? Most of it became public domain a while ago. If a certain percentage of that movie consists of content which has since become public domain, they could be left with nothing but redistribution rights. Trust fund trading however swaps around and gambles modern millions over future billions, and that's who is behind all of this more than likely